Abstract : Results of a study to investigate techniques for assuring Category III localizer signal integrity for roll-out guidance indicate that a surveillance method supported by sterilization of specific areas on and near the runway and quality near and far-field monitoring provide the best tradeoff between quality control and practical implementation. A precision, portable localizer detector to provide accuracies of 0.0005 DDM needed for assessing localizer signal quality with respect to ICAO 0.005 DDM standards has been designed, built, and successfully tested. (Author)